Hi, Brian...I'm new to this forum, but I read your post and did a little searching.
Don't know if you solved your trailer harness problem, but here is a link to a site that appears to have an adapter
for a 7 pin to 4 pin trailer wiring hook-up (specifically for a 2017 Ridgeline). It's the sixth item from the top of the page...
hope this helps!https://www.realtruck.com/curt-unive...17Y1071MA.html